A changing hydrological regime: Trends in magnitude and timing of
glacier ice melt and glacier runoff in a high latitude coastal watershed
Abstract
With a unique biogeophysical signature relative to other freshwater
sources, meltwater from glaciers plays a crucial role in the
hydrological and ecological regime of high latitude coastal areas.
Today, as glaciers worldwide exhibit persistent negative mass balance,
glacier runoff is changing in both magnitude and timing, with potential
downstream impacts on infrastructure, ecosystems, and ecosystem
resources. However, runoff trends may be difficult to detect in coastal
systems with large precipitation variability. Here, we use the coupled
energy balance and water routing model SnowModel-HydroFlow to examine
changes in timing and magnitude of runoff from the western Juneau
Icefield in Southeast Alaska between 1980 to 2016. We find that under
sustained glacier mass loss (-0.57 +/-0.12 m w.e. a-1), several
hydrological variables related to runoff show increasing trends. This
includes annual and spring glacier ice melt volumes (+10% and +16%
decade-1) which, because of higher proportions of precipitation,
translate to smaller increases in glacier runoff (+3% and +7%
decade-1) and total watershed runoff (+1.4% and +3% decade-1). These
results suggest that the western Juneau Icefield watersheds are still in
an increasing glacier runoff period prior to reaching ‘peak water.’ In
terms of timing, we find that maximum glacier ice melt is occurring
earlier (2.5 days decade-1), indicating a change in the source and
quality of freshwater being delivered downstream in the early summer.
Our findings highlight that even in maritime climates with large
precipitation variability, high latitude coastal watersheds are
experiencing hydrological regime change driven by ongoing glacier mass
loss.